The electric field of a propagating electromagnetic wave has two linear components that are orthogonal to one another. Typically, these components trace out an ellipse as a function of time. However, the electromagnetic wave might have only a single electric field component, in which case the electromagnetic wave is said to be linearly polarized.
If an electromagnetic wave is linearly polarized, signal quality may be adversely affected by multipath signals, since many linearly polarized signals with different polarization might exist at the receiving antenna. A polarization diverse antenna can be used to improve signal transmission/reception quality in multipath environments since the signal strength received by such antennas can be greater than with a single linearly polarized antenna. A polarization diverse antenna can also be used to increase network capacity since multiple signals of the same frequency, but different polarizations, can be transmitted from and/or received at a single antenna.
Conventional linear polarization diversity antennas may have two feed/receive lines that transmit/receive two respective orthogonal components of the electromagnetic wave. For example, Zhang (U.S. Pat. No. 6,593,891) describes a polarization diverse antenna that comprises a dielectric substrate having an upper conductive surface. A cross-shaped slot is formed in the upper conductive surface. The lower surface of the dielectric includes elongated conductive strips that are aligned with the arms of the slot, and a rectangular conductive portion that is aligned with the centre of the slot. The antenna also includes a pair of feed lines, each attached to a respective one of the conductive strips.
Alternately, a linear polarization diversity antenna may have a single feed/receive line, but have a complex structure to transmit/receive the orthogonal components of the electromagnetic wave. For instance, Thudor (U.S. Pat. No. 7,336,233) describes a polarization diverse antenna that comprises five slots that are arranged in a H-shaped structure on the upper surface of a dielectric substrate. A single feed line is disposed on the lower surface of the dielectric substrate, and is perpendicular to the centre slot. The antenna also includes a switching means that are positioned in the middle of each slot, except the middle slot. Similarly, Milyakh (U.S. Pat. No. 7,358,916) describes a polarization diverse antenna that comprises four right-angled bent conductive strips that are disposed on a dielectric substrate. The antenna also includes a switching network comprising diodes that are formed between the ends of adjacent strips. A single feed line is connected between the diagonally opposite strips, at the bent portion thereof.
A common problem of dual-polarized antenna is the high possibility of cross-talk between the polarized components.